This invention relates to an improved fitting for asbestos-cement pipe and a method for forming the fitting.
Asbestos-cement pipe is in wide use and especially for very large diameter pipe, for example from 6 inches to 60 inches and even larger. When used in city piping or in irrigation schemes or even with other fluids than water, it is necessary to join the long sections of asbestos-cement pipe together by fittings. There is a wide variety of such fittings, so that they generally have to be made up for each job; it is rarely feasible to carry in stock enough fittings of the wide variety of pipes and sizes needed. Thus, there are elbows, straight coupling sections, tees, angled sections, reducing sections, and so on.
These fittings have been made heretofore by taking cement-lined iron pipe and cutting it off in sections, sometimes welding sections together, as for making elbows and angles, sometimes cutting openings through the side wall, and in all instances having some means for coupling at the end, or at least at one end.
Heretofore, the fittings have been provided with a coupling end by using cast iron pipe sections that are machined down or provided with some type of bolted joint to give the accurate tolerances needed. The importance of the accuracy of the tolerances is a point well worth considering. The manufacturers provide asbestos-cement coupler members, which are in effect cylindrical members of asbestos-cement having two spaced interior annular grooves. In each of these is inserted an O-ring or suitable ring gasket which is to provide the seal, for if the pipe leaks at its couplings, it is of course completely unsatisfactory. The asbestos-cement couplers are made up in large number and are identical for any one particular size, so that they are carried in stock and must be uniform. However, the problem there has been that since they are thus made and are made quite accurately, the members that cooperate with them must likewise be made quite accurately. They must be round and not distorted into an oval or elliptical or irregular shape, and the tolerance is typically kept within twenty or thirty thousandths of an inch.
Since the individual coupling sleeves have had to be made individually, the tolerances have been achievable only by machining and even when achieved, have been very difficult to maintain. When the machined metal ends are welded on to the cement-lined iron pipe, the heat of welding has tended to distort them, and although the distortion may be slight from a visual standpoint, it is too much to be tolerated and still prevent leakage at the couplings. Thus, although machining is expensive and is quite accurate, the results are often nullified by the necessity of the later welding to the main iron pipe. After these elements are put in, and in many cases are lined with cement, there is still a further difficulty in keeping them round, due to the cooling and other factors met, and manufacturers have often welded steel bars, sometimes two or three, across the mouth of this machined sleeve in order to maintain it in round during the initial welding. However, these bars have to be cut off before use and whether cut off in the field or elsewhere, the very heat needed to cut them off with a welding torch results in the danger of distortion again, and they may go out of round.
In my U.S. Pat. No. 3,738,689, issued June 12, 1973, is disclosed one solution to the problems of joining cement-lined pipe. A spin-formed generally cylindrical metal end fitting or spigot is welded to the end of a pipe section and then lined with asbestos-cement itself, for assembly into an asbestos-cement coupler member of the type discussed above. The fitting includes a step in its outside diameter providing an annular stop for seating against the coupler-retained elastomeric ring gasket, which is compressed against the cylindrical outside surfaces of the fitting adjacent to the step. This construction has had the advantage of producing stronger joints with more accurate dimensional control, due to increased strength and heat-deformation resistance caused by spin-forming of the relatively light gauge fittings. However, the assembly nonetheless involves the use of asbestos-cement coupling members which are relatively large in external diameter compared to the pipe sections, and require two elastomeric ring gaskets for each joint, as well as close internal dimensional control for secure joints.